1. Field of the Invention
The present invention relates to a technology for searching similar information by registering information and a feature amount in a corresponding manner and comparing feature amounts of different pieces of information.
2. Description of the Related Art
In recent years, a similar image search technology that searches for an image similar to a specific image from image database based on the specific image has been proposed and realized as a market product.
Generally, in the similar image search technology, an image feature amount, which is information representing features of an image extracted from the image, is registered with a corresponding image at the same time. When a similar image is searched for, a similarity between the feature amounts of images is determined, and an image whose similarity is associated with an image feature amount larger than a predetermined threshold is searched for as the similar image.
As for an extraction method of an image feature amount, for example, Japanese Patent Application Laid-Open No. 2000-187731 proposes a feature amount extraction technology to automatically extract a feature amount corresponding to human sense, so as to allow a search for a similar image compatible with the similar sense that human being feels.
In such a similar image search technology using an image feature amount, the image feature amount is extracted and kept at the time of image registration, and a search can be performed only with the use of the feature amount without referring to the image at the time of the search, and therefore, a search for similar image information can be performed at relatively high speed.
However, in the similar image search technology, every similarity between image feature amounts of all registered images to search for is to be calculated at the time, which causes a problem that as the number of registration images increases, the search process speed decreases.